Section 20.—COMPENSATING AND BALANCE WEIGHTS.
It is of the utmost importance that every revolving or reciprocating part of any machine should be as nearly as possible balanced, to obtain smooth running with the least amount of wear.
The following are types of the most important devices and their applications:—
[369]. Balanced lever, having a sliding cheese or ball weight fixed with a set screw.
[370]. Balanced cage of hoist. It is usual to over-balance the cage to divide the work between the up and down journeys in hand-power lifts to assist the load; but in power and hydraulic lifts the cage is under-balanced so as to descend when empty.
[371]. Hydraulic balance lift, in which the dead or constant load of cage and ram are nearly balanced by a loaded piston in a supplementary cylinder; to raise the loaded cage the pressure water is admitted to the upper side of this piston. Many varieties of this type are in use; see Ellington’s, Johnson’s, Stevens and Major’s, Waygood’s, and other patent lifts.
[372]. Variable volute compensating balance for revolving shutters, blinds, curtains, &c., to maintain an even balance in all positions, The weight chain is as thick as the coiling shutter on blind, so that the acting radii of the shutter and weight are always proportional.
[373]. Variable compensating balance for hydraulic lift rams, to compensate for loss of immersion of the ram as it ascends (Berly’s patent). See also Stevens & Major’s patent, where bell-crank levers and weights are employed instead of loaded chains. See [No. 383].
[374]. Balanced fly-wheel. For balanced cranks, see [Nos. 172] & [173].
[375]. Increasing balance by sections, lifted at intervals as the chain rises.
[376]. Balanced riveting machine. See Tweddell’s patents.
[377]. Variable lever balance. For balanced cranes, see [Section 18].
[378]. In deep lifts, to balance the weight of chain or rope, it is made endless.
[379]. Another method. The loose chain hung from cage is of the same weight per foot as the lifting chain.
[380]. Balance weight on a screw arm for adjustment, employed on weighing machines.
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[381] & [382]. Worthington’s compensating air cylinders, employed on direct-acting horizontal pumps, working expansively, in lieu of fly-wheel. The oscillating or vertical cylinders are air or spring pistons, absorbing power the first part of stroke and giving it out during the latter part.
[383]. Variable balance weight by bent lever.
[384]. Variable balance weight by double links and sliding joints.
[385]. Dawson’s compensating governor. See Mechanical World, August 25th, 1888.
[386]. Balanced doors, hinged vertically.
[387]. Balanced sashes, or vertical sliding doors.
[388]. Method of balancing a bloom in charging or withdrawing from a furnace, or any similar use.
[389]. Balance for link motion.
[390]. Weight to keep a cord or rope in tension.
[391]. Mode of balancing two sliding doors so that they rise and fall at proportionate speeds.
Hoisting and winding engines (see [Nos. 1222], [1223]) are balanced by having an ascending and descending cage, and two ropes, one winding on as the other winds off the drums.
Double cage hoists similarly balance themselves. Heavy slide valves, and other reciprocating parts of steam engines, are balanced by small steam pistons. See [Nos. 1651]-[1654].
Foot treadles, when required to always stop at a point off the dead centre, have a balance weight fixed to fly-wheel, at right angles to the dead centre.
A water tank is often used to serve as a counterpoise, or balance, and may be made variable by varying the quantity of water by a siphon or other device.
For Balanced Valves, see [Section 89].